Cardiovascular System Flashcards
How is the heart positioned?
- Oblique, rests on diaphragm.
- Two-thirds lies left of the midsternal line, between rib 2 and intercostal 5
- base points to right shoulder
- apex points to left hip
Where is the heart located?
ventral, thoracic, mediastinum, pericardial cavities
List the three layers of the heart membrane and describe what they are made of and what there purpose is.
SUPERFICIAL FIBROUS PERICARDIUM - outermost layer of dense connective tissue that protects, anchors, and prevents overfilling with blood.
DEEP TWO LAYERED SEROUS PERICARDIUM - parietal layer lines the internal surface of the fibrous pericardium. the visceral layer (epicardium) lies on the external surface of the heart. Both produce lubricating serous fluid to fill the space between them.
What are the three layers of the heart wall?
epicardium
myocardium
endocardium
What is the epicardium?
The visceral layer of the serous pericardium.
it is the outer layer containing squamous epithelium and connective tissue.
It contains blood, lymph, and nerve supply and produces serous fluid to reduce friction
What is the myocardium?
spiral bundles of cardiac muscle cells.
contains a fibrous network of collagen and elastin fibers that anchor cardiac muscle fibers (allows the heart to maintain its structure), support great vessels and valves, and limits the spread of action potentials to specific paths
FUNCTION: contract to pump blood throughout the body
What is the endocardium?
Squamous epithelium over connective tissue
innermost layer of the heart
FUNCTION: provides a smooth surface for blood to flow over.
What are the three surface grooves and what is there purpose?
PURPOSE: carry coronary blood vessels to heart wall
Antrioventricular sulcus
Anterior interventricular sulcus
Posterior interventricular sulcus
Describe the atria
walls are ridged by pectinate muscles (receiving chambers) separated internally by the interatrial septum into left and right
FUNCTION: receive blood and pump blood into ventricles (30% pumped and 70% passive movement)
Contain AURICLES: protruding appendages that increase atrial volume
What vessels enter the right atrium?
Superior vena cava
Inferior vena cava
Coronary sinus
What vessels enter the left atrium?
Right and left pulmonary veins
What is the differences between veins and arteries?
Veins bring blood away from heart and arteries bring it to the heart
describe the ventricles
- separated by the interventricular septum
- anterior and posterior interventricular sulci mark the position of the septum externally
- the ventricles make up most of the heart
- wall is much thicker than atria (more muscular)
- contain trabeculae carneae and papillary muscles
What are the trabeculae carneae?
they are irregular ridges of muscle in the left and right ventricle
What are the papillary muscles?
they are cone like muscles anchor the chordae tendonae of valves.
contract just before the ventricles to take up the slack in the chordae tendonae and prevent valves from being pushed open backwards into the atria.
Describe the function and structure of the left ventricle.
receives oxygenated blood from the pulmonary veins and pumps blood through aorta to systemic circuit
wall is thicker than right ventricle
dominates posteroinferior surface
Describe the function and structure of the right ventricle
Receives de-oxygenated blood from: vena cava and pumps blood through the pulmonary trunk to the pulmonary circuit
thinner wall then the left ventricle
Describe the pulmonary circuit
it is short, low-pressure circulation that moves blood to and from lungs for gas exchange between air and blood.
right ventricle -> pulmonary -> semilunar valve -> pulmonary trunk -> pulmonary arteries -> capillaries of lungs -> pulmonary veins -> left atrium -> left AV valve -> left ventricle
Describe the systemic circuit
is a long, high pressure circuit with high resistance in the long pathways. Moves oxygenated blood to and from tissues for gas exchange between blood and tissue cells
left ventricle -> aortic semilunar valve -> aorta -> systemic arteries -> tissue capillary beds -> systemic veins -> vena cavae -> right atrium -> right AV valve -> right ventricle
What is coronary circulation?
it is the blood supply to the heart muscle itself.
Myocardium muscle has high ATP demand
the arterial supply varies considerably from person to person
KNOW THE ARTERIES AND VEINS
What is an anastomose?
Junctions among branches in the arterial supply of the coronary circulation.
These fusing networks provide collateral routes for blood delivery to the heart muscle
Explain and describe angina pectoris.
it is acute thoracic pain caused by a temporary blockage in blood supply to the myocardium.
Temporary lack of O2 weakens cells but does not kill them
Explain and describe myocardial infarction
HEART ATTACK
prolonged coronary blockage -> prolonged lack of O2 -> cells die -> repaired with non contractile scar tissue
prognosis depends on extent and location of damage (left ventricle which is the systemic pump is more serious)
What is the purpose of heart valves?
to ensure the unidirectional blood flow through the heart (no back flow)
What controls the opening and closing of the valves of the heart?
changes in blood pressure (no nerves involved)
What are the two sets of valves in the heart?
Atrioventricular (AV) valves
Semilunar (SL) valves
Describe the atrioventricular (AV) valves
RIGHT AV VALVE: tricuspid
prevents back flow into the right atrium when right ventricle contracts
LEFT AV VALVE: bicuspid or mitral valve
prevents back flow into left atrium when left ventricle contracts
What are the chordae tendineae?
They are tiny white collagen fibers that anchor the AV valve cusps to papillary muscles.
Prevent valves from being blown up into the atria (in combination with the papillary muscles
Describe the semilunar (SL) valves.
right (pulmonary) SL valve: prevents backflow into right ventricle when ventricle relaxes
left (aortic) SL valve: prevents backflow into left ventricle when ventricle relaxes
The heart beats in a lub-dup pause. explain what these sounds are associated with.
1st sound: closing of AV valves - start of ventricular systole (contraction)
2nd sound: closing of SL valves - start of ventricular diastole (relaxation)
What are heart murmurs and what do they indicate?
they are abnormal heart sounds and are most often indicative of heart valve problems.
Which valves close first?
LAV closes before RAV
Aortic SL closes before pulmonary SL
What are leaky valves?
valves do not close properly. results in murmers and turbulence in flow of blood.
heart will have to work harder because it loses some pressure in back flow.
What is stenosis?
it is the narrowing of the vessels. results in impeded flow of blood
What are some of the microscopic characteristics of heart muscle cells?
striated, short, fat, branched, uninucleate, connected by intercalated discs
connective tissue matrix (endomysium) fillc the intercellular space connects to the fibrous skeleton (which provides something to pull and exert force against)
T-tubules are wider but less numerous and SR is simpler than in skeletal (has no terminal cisternae)
Numerous large mitochondria (25-35% cell volume)
contains sarcomeres but more irregular
heart muscle behaves as a functional syncytium (contracts as single unit
What is an intercalated disc?
it is the junction between heart muscle cells
contains:
DESMOSOMES to hold cells together during contraction
GAP JUNCTIONS to allow ions to pass quickly from cell to cell
What are some of the differences in function and physiology of heart muscle compared to skeletal
- about 1% of the cells are autoexcitable: pacemaker cells
- Rest of cells are contractile: pump
- has no motor groups; entire muscle contracts or not at all
- long refractory period to enable pumping
Explain what pacemaker cells are.
Specialized cardiac cells that initiate and distribute impulses, ensuring that the heart depolarizes in an orderly fassion.
these autorhythmic cells have an unstable resting potential called pace maker potential that continuously depolarizes
Explain the process of the generation of the AP in the pacemaker.
resting potential is -60mv
slow depolarization to threshold potential (-40mv) due to open slow Na+ channels
fast calcium channels open when threshold potential is reached and Ca2+ rapidly enters the cell
membrane rapidly depolarizes further and generates an action potential
Ca gates shut, K+ gates open releasing K+ from cell and repolarization occurs as charge difference is regained
AP is transmitted to rest of myocardium via intrinsic cconduction system
heart contracts. Atria first then ventricles
What is the intrinsic conduction system?
the heart contains its own conduction system that is independent of the nervous system.
Although the heart beat can be altered by nerve impulses, if all the nerves to the heart were severed, the heart would still beat
It speeds up the impulse through the heart synchronizing the muscle cells to contract closer to the same time increasing pumping effectiveness
What is the order of excitation of autorhythmic cardiac cells?
SINOATRIAL (SA) NODE (PACEMAKER): generates impulses 75 times every minute (sinus rhythm). Depolarizes faster than any other part of the myocardium and is therefore the hearts pacemaker
INTERMODAL PATHWAY: depolarization wave spreads via gap junctions and these specialized tracks to AV bundle
ATRIOVENTRICULAR (AV) NODE: smaller diameter fibers; fewer gap junctions which delays impulses about 0.1s allowing atria to complete contraction before the ventricles contract.
ATRIOVENTRICULAR (AV) BUNDLE (BUNDLE OF HIS): The only electrical connection between the atria and ventricles. Branches into….
RIGHT AND LEFT BUNDLE BRANCHES: two pathways in the interventricular septum that carry the impulses toward the apex of the heart.
PURKINJE FIBERS: complete the pathway from the interventricular septum through the apex and curving back into the atrioventricular walls.
How often does the SA node depolarize?
75/min making it the fastest rate of depolarization
this makes it the pacemaker of the heart
How often does the AV node depolarize in the absence of the SA node?
60/min
How often do the purkinje fibers depolarize in the absence of the SA node?
40/min
What is the sinus rhythm?
the rhythm that is generated by the SA node (75 times/min)
What is the sequence of stimulation and contraction?
SA node develops pacemaker potential which is transmitted to walls of the atria
Atria begin to contract
Impulse delayed at AV node to allow complete contraction of atria before contraction of ventricles
ventricles then contract
produces normal sinus rhythm
What is arrhythmia?
irregular heart rhythms
What are the 5 homeostatic imbalances in electric conduction of the heart?
UNCOORDINATED atrial and ventricular contractions
FIBRILLATION: rapid, irregular contractions which are useless for pumping blood
DEFECTIVE SA NODE may result in: Ectopic focus (abnormal pacemaker takes over) if AV node takes over there will be a JUNCTIONAL rhythm (40-60 bpm)
DEFECTIVE AV NODE may result in: Partial or total heart block where few or no impulses from the SA node reach the ventricles causing ventricles to beat at different rate than atria
TOO MUCH COFFEE OR NICOTINE - PVC (extra systole). Premature ventricular contraction.
explain the process of contraction in the contractile cells.
membrane starts out as being polarized. Active pumps eject Na+ and bring in and K+ brought in.
action potential (generated by pacemaker) reaches the contractile cell
Na gates open allowing Na to rush into the cell causing depolarization (it is a positive feed back loop)
slow Ca2+ channels in the sarcolemma open with the depolarization allowing small amount of Ca2+ in (begins slight contraction)
Na+ gates shut
the increase in Ca2+ concentration causes a quick release of Ca2+ from the SR
Ca2+ binds to troponin
crossbridges form, myofilaments slide (contraction)
Slow Ca2+ gates stay open to keep [Ca2+] high and K+ permeability decreases to create a DEPOLARIZATION PLATEAU
K+ gates open releasing K+ from the cell resulting in repolarization
long absolute refractory period - the inexcitable period when Na+ channels are still open or inactivated
What is the absolute refractory period?
it is the long inexcitable period when Na+ channels are still open or inactivated. this prevents tetany which would stop the hearts pumping action
What does heart function depend on?
aerobic respiration to supply ATP
good supply of oxygen and fuel
adequate blood supply
What is ischemia?
blockage of coronary arteries leading to deficient oxygen supply to the myocardium.
Why is oxygen the biggest influencing factor for cariac muscle?
cardiac muscle is very adaptable and can switch pathways as needed to use whatever fuel is available, but always needs oxygen.
What is an electrocardiogram (ECG or EKG)
it is a graphic record of all the action potentials generated by nodal and contractile cells at a given time (not a single AP)
What are the three distinguishable waves of an ECG
P WAVE - depolarization of the atria
QRS COMPLEX - depolarization of the ventricles
T WAVE - repolarization of ventricles
What happens in the PQ interval?
the beginning of atrial excitation to beginning of ventricular contraction
What occurs in the ST segment?
entire ventricular myocardium depolarized. this is where the AP plateau’s
What occurs in the QT interval?
beginning of ventricular depolarization to repolarization
What does systole refer to?
the period of contraction (note there are atrial and ventricular systole)
What does diastole refer to?
the period of relaxation (both atrial and ventricular)
List the phases of the cardiac cycle and describe what happens in each.
VENTRICULAR FILLING - occurs mid to late diastole
AV valves are open, 70% of blood passively flows into ventricles. Atrial systole occurs at end of this phase delivering remaining 30%. End diastolic volume (EDV) is reached
VENTRICULAR SYSTOLE:
atria relax and ventricles begin to contract. Rising ventricular pressure results in closing of AV valves. Volume remains constant because pressure is less than that of the arteries and Isovolumetric contraction phase occurs. Pressure continues to increase until it exceeds areteries forcing SL valves open ejecting blood. Volume of blood remaining in each ventricle is called end systolic volume (ESV)
ISOVOLUMETRIC RELAXATION: occurs in early diastole
ventricles relax. Backflow of blood in aorta and pulmonary trunk closes SL valves and causes dicrotic notch (brief rise in aortic pressure)
QUIESCENT PERIOD:
both atria and ventricles are relaxed - lasts about 0.4 secs
What is end diastolic volume (EDV)?
the maximum volume of blood in each ventricle prior to contraction
this volume occurs at the end of the ventricular filling phase
What is the isovolumetric contraction phase?
the phase in ventricular systole where AV valves are closed and the blood pressure is less than that in the large arteries so the SL valves stay closed and the volume remains constant until the pressure forces open the SL valves
What is the end systolic volume (ESV)?
the volume of blood remaining in each ventricle after contraction.
How long does atrial systole, ventricular systole, quiescent, and the total cycle last?
atrial systole 0.1 sec
ventricular systole 0.3 sec
quiescent 0.4 sec
total cycle 0.8 sec
What does HR mean?
number of beats per minute
What does SV mean?
volume of blood pumped out of ventricle with each beat (stroke volume)
What is cardiac output?
volume of blood pumped by each ventricle in one minute
CO = HR x SV
What is cardiac reserve?
it is the difference between resting and maximal CO
maximal CO - resting CO
usually 4-5 times resting CO
How do you calculate the stroke volume (SV)?
EDV - ESV = SV
end diastolic volume - end systolic volume = stroke volume
What are the three main factors that affect SV?
PRELOAD: degree of stretch of cardiac muscle cells before they contract. EDV is inc by slow heart beat and exercise. EDV is decreased by a rapid heart rate and decreased blood volume
CONTRACTILITY: increase in force of contraction that is independent of stretch and EDV. Caused by more Ca2+ ions from SR and extracellular fluid.
AFTERLOAD: pressure that must be overcome for ventricles to eject blood. Back pressure in vascular system makes it harder for ventricles to empty. inc with hypertension which limits the reduces the ability of ventricles to eject blood.
What is the Frank-Starling law of the heart?
states that the more the heart muscle is stretched prior to contraction, the harder it will contract. (Greater EDV, the greater the force of contraction)
Explain what positive and negative inotropic agents do and give some examples.
POSITIVE INOTROPIC AGENTS: agents that inc contractility. Ex. sympathetic nervous system release of norepinephrine
NEGATIVE INOTROPIC AGENTS: acidosis. increased extracellular K+ levels. Ca2+ channel blockers
What are positive and negative chronotropic factors?
pos = factors that increase HR neg = factors that decrease HR
What are the two ways the body regulates heart rate?
Autonomic nervous system regulation
Chemical regulation
Describe some of the characteristics of the autonomic nervous system as it relates to the heart
cardiac centers are located in the medulla oblongata:
- Cardioaccelatory center innervates SA and AV nodes, heart muscle, and coronary arteries through sympathetic neorons.
- Cardioinhibitory center inhibits SA and AV nodes through parasympathetic fibers in the vagus nerves
both of these are firing at the same time, inhibitory is slightly more dominant
- Baroreceptors - these are receptors that can detect changes in blood pressure and which stimulate or inhibit accelatory or inhibitory.
Give an example of baroreceptros.
Atrial brainbridge reflex: stretching of atrial walls stimulates the SA node and sympathetic reflexes
inc venous return -> inc atrial pressure -> stimulates stretch receptors -> sympathetic nervous system -> inc HR and force of contraction
what is the sympathetic nervous system, what is it mediated by and what tends to activate it?
it is a positive chronotrope
Fight or flight : emotional or physical stressors
mediated by norephinephrine
What is the parasympathetic nervous system, what is it mediated by, and what nerve does it use?
It is a positive chronotrope that counteracts the sympathetic effects that slows the HR to the normal 75 (would be 100 without it)
it is mediated by acetylcholine (ACH)
and uses vagus nerves
Explain how the body chemically regulates heart rate.
HORMONES:
EPINEPHRINE from adrenal medulla enhances heart rate and contractility.
THYROXIINE inc HR and enhances the effects of norepinephrine and epinephrine
INTRA AND EXTRACELLULAR ION CONCENTRATIONS:
normal levels of ions must be maintained for normal heart function
Hypercalcemia (Ca2+) - inc HR
Hypocalcemia - dec HR
Hyperkalemia (k+) - leads to heart block and arrest
Hypokalemia - feeble HR
hypernatremia (Na+) - decreased HR
What are some general factors that can influence HR?
Age - dec with age
Gender - faster in females
Exercise - dec average HR
Body temperature - inc HR by inc metabolic rate
What is tachycardia?
abnormally fast HR >100 bpm
if persistent, may lead to fibrillation. May result from elevated body temp, stress, drugs, or heart disease.
What is bradycardia?
abnormally slow HR < 60 bpm
results in inadequate blood circulation. May be a desirable result of endurance training (in that case CO remains the same due to heart hypertrophy)
What is congestive heart failure (CHF)?
progressive condition where cardiac output (CO) is so low that blood circulation is inadequate to meet tissue needs
What are three causes of congestive heart failure (CHF)?
Coronary atherosclerosis: blockage of arteries with fatty deposits
Persistent high blood pressure: weakens the heart
Multiple myocardial infarcts: contractile cells replaced by scar tissue
Dilated cardiomyopathy (DCM) - ventricles enlarge, myocardium deteriates causing loss of ability to contract (can be caused by drugs like alcohol, cocaine, excess adrenaline. Or by inflammation after infection)
Explains what happens if the left side of the heart fails.
it causes pulmonary congestion
blood accumulates around lungs. fluid leaks into lungs
Explain what happens if the right side of the heart fails.
it causes systemic congestion - edema
blood accumulates at extremities. fluid leaks into interstitial spaces and tissues.
What are 4 age related changes affecting the heart?
SCLEROSIS AND THICKENING of valve flaps: valves cannot close tightly causing backflow
DECLINE IN CARDIAC RESERVE: heart has less ability to respond to stress
FIBROSIS OF CARDIAC MUSCLE: muscle replaced by scar tissue resulting in inefficient pumping
ATHEROSCLEROSIS - artery blockage (usually caused by diet). results in hypertensive heart disease and occlusion of coronary arteries
What are the two factors the contribute to the creation of an AP plateau in cardiac cells?
Slow Ca2+ gates stay open allowing Ca2+ to keep entering cell prolonging depolarization
K+ permeability decreases which prolongs the plateau and prevents rapid repolarization.
What is the purpose of the plateau in the AP in cardiac contraction?
Allows the cell to contract further (for longer duration) in order to more effectively pump.
